On Thu, Aug 12, 2010 at 1:47 PM, ikjtel <ikj12...@yahoo.com> wrote: > I've run a comparison test of > - the "old" GR dqpsk block > - the "new" one (dqpsk2) > - the "op25" cqpsk (Gardner/Costas) block > > The resulting constellation diagrams are viewable at > http://www.lightlink.com/mhp/qpsk2/ > > The results are: Gardner is the winner, the old GR blocks take second, the > new ones are last > (intriguingly as shown in the symbol plot, things seem to start off nicely > but then go awry)... > > The problem could be caused by dumb user error - D.U.E. (TM) or something > fixable by simple > parameter tweakage? > > The input file used in all three cases is a complex capture taken from a > system using so-called > "LSM/CQPSK". Basically, that appears to mean something like: a) simulcast > distortion is added; > b) PI/4 DQPSK is used; c) pulse shaping is stretched so as to fit the > bandwidth of the signal into > a 12.5 KHz channel; d) a "non-standard" waveform is used which results in the > signal passing > through the origin (0,0) point, introducing a rather severe AM component. > > There are two further wrinkles in this particular case which should be noted: > 1) the complex file was captured using a "very poor man's USRP", *not* a real > USRP > [ see http://www.lightlink.com/mhp/iq/ ]. However the file formats are > fully compatible. > Further, a DBSRX capture exhibits all the same characteristics. > 2) the receiving location is outside the designed coverage area of the system > > The results of all of this, plus the fact that the capture was made prior to > verifying that the > hardware even was functional for LSM, makes for a very "difficult" specimen > (perfect for > torture-testing RX codes)... > > Best Regards > > Max
That's a very interesting result. Theoretically, it makes sense for the Gardner loop to perform better than the M&M, but the polyphase filterbank approach will perform better than both. This suggests either an error in the parameters you chose or a bug in the code. When I'm fully setup with multiple USRPs to do over-the-air testing again, I'll investigate farther. Tom _______________________________________________ Discuss-gnuradio mailing list Discuss-gnuradio@gnu.org http://lists.gnu.org/mailman/listinfo/discuss-gnuradio
